"Radiologic Diagnostic Oncology Group V: Stereotactic Biopsy for Nonpalpable Breast Lesion Characterization" This plan is a cooperative effort from a consortium of ten institutions in response to RFA:CA 93-01. Our proposal addresses the scientific research and coordination of the clinical consortium component of this RFA. The group comprises experienced investigators and clinical experts from the following institutions: University of Arizona, Johns Hopkins, Yale, UCLA, University of Virginia, Memorial Sloan-Kettering, Emory, Radiology Imaging Associates, Deaconess Hospital, and Case Western University. The overall objective of this plan is to develop a clinical decision matrix for the evaluation and diagnosis of nonpalpable breast lesions that would be generally applicable to a broad spectrum of institutions. The algorithm will be derived from optimized input criteria that enhance diagnostic accuracy, reduce noise (variation) and result in favorable health outcomes, cost-benefit ratio and cost effectiveness. The Specific Aims of this proposal are: (1) Compare the accuracy and efficacy of stereotactic fine needle aspiration cytology (SFNAC) and stereotactic core needle biopsy (SCNB) with surgical breast biopsy (SBB) for diagnosis and management of nonpalpable (subclinical) breast lesions. These metrics will be tested for two applications: a) management of "indeterminant" lesions with low to moderate probability of malignancy as an alternative to follow-up mammography, and b) diagnosis of breast cancer and potential replacement of surgical breast biopsy. (2) Identify optimal, standardized approaches to lesion selection, stereotactic imaging, stereotactic needle sampling and cytologic and histologic diagnosis. (3) Evaluate the impact of patient-related factors such as risk for breast cancer, attitudes and perceptions regarding stereotactic breast needle biopsy (SBNB) versus SBB, and morbidity for the three diagnostic modalities (SFNAC, SCNA & SBB) on the proposed decision matrix. (4) Assess the health outcomes and potential resultant costs savings of using SBNB in lieu of SBB to evaluate nonpalpable breast lesions. Formulate data accumulated from this trail into guidelines for clinical practice and protocols for health policy issues.